The MBK centre in Bangkok is great for clothing. I've been wearing a pair of fake Deisel jeans for a year that I bought from there and theyre still going strong. I loved the fact that they shortened them in ten minutes and even finished them with an authentic jeans style hem so you couldnt tell that they had been shortened.

I know things might be cheaper elsewhere in Thailand but at the prices theyre charging youd have to be really low on funds to care.

Also I think the quality of stuff on sale at MBK is slightly better than the stuff on sale along Ko San Road.